Telescoping submarine antenna with capacitive coupling



July 16, 1963 R. s. NICKERSON ETAL 3,098,230

TELESCOPING SUBMARINE ANTENNA WITH CAPACITIVE COUPLING Filed May 22,1961 5 j g I 20 j 25 24 g 22 as arm m l2 34" I2 RICHARD s. NICKER N PAULA. CRANDEL E BY ATTORNEYS 3,098,230 Patented July 16, 1963 ice 3,098,230TELESCOPING SUBMARINE ANTENNA WITH CAPACITIVE COUPLING Richard G.Nickerson, Sudbury, and Paul A. Crandell, Bedford, Mass., assignors toElectronautics Corporalion, Maynard, Mass, a corporation ofMassachusetts Filed May 22, 1961, Ser. No. 111,781 2 Claims. (Cl.343-709) This invention relates in general to antenna systems and inparticular to an antenna system for operation under water.

Antenna systems for submarines present some serious problems to thedesigner. In a typical installation where a retractable antenna is used,it is necessary, of course, that the coupling of the antenna to theradio apparatus be made in such a manner that the antenna is notgrounded to the hull of the ship. Obviously, in an environment of seawater, shorting of the antenna to the hull through the Water isdifiicult to avoid.

The most commonly used system at present is probably that in which acable extends from the radio apparatus to a metal ring which is, inturn, in contact with the base of the antenna. The coupling unit bywhich contact is made is usually enclosed in a housing through which theantenna passes. It is attempted to prevent surrounding sea water fromentering the enclosure between its inner wall surfaces and the antennaby utilizing O-ring seals. This expedient has not yielded satisfactoryresults, primarily because the operating conditions impose severemechanical stresses and hydrostatic pressures against the antenna andthe enclosure. Seepage of sea Water into the protected contact areacauses grounding of the metal rings and disabling of the radioapparatus.

Shot-ting of the antenna itself has been avoided by covering the antennawith a suitable plastic, but moisture leaks such as those describedabove in the coupling area nullify any advantages derived from the useof the plastic covering of the antenna per se. Of course, the fact thatthe an tenna must be retractable simply magnifies the problem ofprotection from shorting in the coupling area.

It is, therefore, the primary object of the present invention to couplean antenna to radio apparatus without shorting due to moisture seepage.

It is another object of the present invention to improve radio operationin submersible vehicles.

It is still another object of the present invention to provide anantenna system suitable for use on a submarine.

The foregoing and other objects are attained in the present invention bycoupling the antenna to the radio apparatus in such a manner that noportion of the RF signal circuit is exposed to contact with surroundingsea water. The coupler between the radio apparatus and the antenna ismade up of a pair of coaxial metal elements which are separated bysuitable dielectrics to form a capacitive connection between the radioapparatus and the antenna. In the coupler, one of the metallic elementsis preferably in rounded by the plastic insulating material of theantenna. The second metallic sleeve and its plastic covering are ofproper dimensions to fit within the first metallic sleeve and itsplastic covering. The dimensions and the spacing of the sleeves are suchthat the coupler adds very little to the impedance seen by thetransmitter of the radio apparatus, and the impedance is of such a valuethat it can be easily compensated for by tuners presently in use. Powerloss of only a negligible amount is encountered in the coupler.

Inasmuch as the inside diameter of the coupler housing and the outsidediameter of the antenna mast are so close, with proper lubricationbetween the two, no objectionable seepage takes place even though theantenna is retractable. In addition, roller assemblies may be providedto maintain the antenna concentric under varying wind and water loadingand to facilitate raising and lowering of the antenna. For a betterunderstanding of the present invention, reference should be made to thefollowing specification of a preferred embodiment thereof, which shouldbe read in conjunction with the appended drawing, the single FIGURE ofwhich is a sectional view, partially cut away, of the antenna, couplingunit and the hull of the submarine.

In the drawing there may be seen a portion of the submarine hull 12 towhich a plastic housing 14 is joined by a series of studs, of which thestud 16 is typical. Usually, the housing is generally cylindrical andthree or more bolts may be used to hold it in place on the hull.

The lower end of the housing 14 is fitted closely and may be sealed intoan opening which is provided in the hull 12. A cable 18 running from theradio apparatus (not shown) is suitably sealed in place in the housing14 with its central conductor 20 in contact with a conduction member 22.The conduction member 22 is threaded into the housing 14 with a suitablesealing ring 23 disposed in the housing and contacted by a cap 24 on theconduction member. The conduction member 22 may be threaded at its endand screwed into a collar 26 brazed or otherwise suitably fastened to ametallic sleeve 28. The metallic sleeve 28 is embedded in the plastic ofthe housing 14 and is concentric with a large opening formed verticallythrough the housing 14. The thickness of the plastic disposed internallyof and lining the metallic sleeve 28 may be of the order of 0.010" to0.125", and preferably 0.025" to 0.050.

Below the ring 32 comes into contact with the stop ring 30 and therupward motion of the antenna mast 34 is thus vented.

Within the projected area of the metal sleeve 28 is a second metalsleeve 36, smaller than and concentric with the sleeve 28. The sleeve 36is embedded within the body of the antenna mast 34 and is covered by alayer of plastic which may be of the order of 0.010" to 0.125", andpreferably 0.025 to 0.050, in thickness. The metal sleeve 36 is formedinto a ring of greater thickness adjacent its upper end, and to that endthere may be soldered or otherwise firmly mechanically and electricallyconnected a mesh screen 38. The screen 38 serves as the activeconductive element running the length of the antenna mast, and it isalso embedded within the plastic of the body of the antenna mast.

The electrical operation of the antenna system is quite efiicient bycomparison to known submarine systems. The same limitations which occurbecause of the shortfurpre-

cant degradation of electrical performance. In presently used submarineantenna systems, the real part of the lmpedance seen by the system atthe input coupler is:

where 8" being the length of the antenna and r its radius. By thismethod, Z is computed to be equal to 318 ohms for a -foot antenna with a25-foot radius.

Calculated values of the impedance, (R+ 'Xa), at the antenna input overa range of frequencies from 2 to 3. megacycles indicate that a largemis-match to the 50- ohm transmitter impedance is presented over much ofthe operating range of the system. The mis-match is compensated for bymeans of an RF tuner which places a variable inductance in series withthe antenna. It should be noted, however, that the tuner compensatesonly for the imaginary component of the impedance and some loss resultsfrom the resistance rnis-match.

The effect of the coupler of the present invention may be computed forcomparison with the input impedances calculated above. If a pair ofconcentric conducting cylinders of infinite length, having an innerradius a and an outer radius b respectively, are considered, it may beconsidered that the electrical displacement is radially outward from theaxis. In these conditions, from Gausses Electrical Flux Theorem, it maybe postulated that:

f,e1 J-TzdS=21rreE=q where q is the total charge, E is the electricalfield and r" is the radius of the cylinder, wherein a r b. Theelectrical field is literally the divergence of the potcntial;therefore,

The potential between the cylinders is:

and, therefore, the capacitance per unit length of a cylindricalcapacitor is:

7 .354 10210 D/d where e is a dielectric constant of 4.5, D is 6.313 andd is 6.187". These dimensional values of inner and outer capacitorplates are based upon an antenna mast diameter of 6.250" which allowsfor a thickness of dielectric between the plates of .125". Greataccuracy may be obtained by calculating the effect of the air gap andthe lubricant that would be present in the antenna coupling of theinvention. Obviously, the over-all capacitance of the condenser isdetermined by the series combination of the capacitances of the threedielectric layers of the gap, the plastic material and the lubricant. Ifthe gap between cylinders is reduced to a minimum, its effect becomesnegligible and may be ignored. In any event, a total capacitance of 1600et. for a coaxial coupler of the type shown having a length of 6" hasbeen computed. The capacitance of the antenna is, of course, in serieswith the capacitance of the coupling device, and the additionalimpedance which it contributes is not only insignificant, but within therange of compensation by the tuners conventionally used.

The voltage gradient in the coupler capacitor is as follows:

AE 5450( SP peak volts where S is the voltage standing wave ratio, P isthe power in kilowatts and d is the radius of the inner plate inthousandths of an inch or mils. The gradient reaches a value of 1.2 peakvolts per thousandth of an inch of thickness, assuming a voltagestanding wave ratio of 4 to 1, an input of 1 kilowatt into the coaxialcoupler, and a characteristic impedance 2,, of the coupler of about .65ohms. The breakdown voltage in the plastic insulating material is about62 volts per thousandth of an inch of thickness which insures a marginof safety of approximately to 1. Capacitors of this type or of evensmaller diameters have been found to operate safely up to 10,000 voltswithout breakdown.

At the highest frequency of operation, the dissipation factor of thedielectric may cause a power loss of as much as 2 percent. Such a lossis not significant when considered with all other system losses.

Although the housing of the coupler as a preferred embodiment of theinvention has been made up of glassfabric resin laminates as has theplastic body of the antenna mast itself, other materials may besuccessfully used. A typical glass fabric suitable for the purposes ofthe invention may be glass-fabric having a Garan or Volan finish, andany one of several weaves may be used such as 181, 18ll50, 164l50, 121or even woven roving. The resin may be epoxy, polyester, phenolic orsilicone. Other resins may also be used, but ease of fabricationsuggests the foregoing materials as being preferred. Obviously, suchmaterials as Teflon, polyethylene, modified polystyrenes andpolyurethanes may also be used in conjunction with suitable catalystsknown in the art.

The metal from which the coupler sleeves and the mesh element of theantenna are made may be any low resistance conductive material. Copper,brass, aluminum, steel and various alloys are satisfactory. The sleevesare embedded between layers of the glass-resin fabric, and the onlycritical structure requirements are in maintaining the proper spacingbetween the capacitor plates formed by the sleeves. In other words, thethickness of the material surrounding the antenna mast sleeve and ofthat lining the housing sleeve must be carefully maintained. It is alsodesirable that the metal be carefully cleaned before it is embedded inthe surrounding plastic in order that suitable adhesion may take place.

Although what has been described constitutes a preferred embodiment ofthe invention, other suitable structures within the scope of theinvention will suggest themselves to those skilled in the art upon areading of the foregoing specification. By way of example, rather thanlimitation, a flat strip of metal might be wound in the form of a helixwithin the plastic section of the base of the antenna mast. A secondhelix might be contra-Wound within the coupler housing, the end of thesecond helix being directly connected to the end of the cable from theradio apparatus. In this alternative, as in the preferred embodimentdescribed above, no contact is possible between the active elements andthe surrounding sea water by reason of their embodiment in the plasticinsulating material. This and other alternative structures wherein theactive coupler elements are completely prevented from contact with apotentially shorting environment are believed to be within the spiritand scope of the present invention, which should be limited only asnecessitated by the breadth of the following claims.

What is claimed is:

1. An antenna system for a submarine in which at least a portion of saidsystem is normally submerged comprising an insulating housing, a cablefixed in said housing, a first conductive sleeve connected to said cablefor RF energy transfer therebetween, said first conductive sleeve beingembedded in said housing, said housing having an opening formedtherethrough concentric with said first conductive sleeve, and anantenna mast movable in said opening, said antenna mast being formed ofinsulating material, an antenna element and a second conductive sleeveembedded in said insulating material, said second conductive sleevebeing electrically connected to said antenna element, a capacitivecoupler of energy between said cable and said antenna element beingformed by said first and second conductive sleeves.

2. An antenna system for a submarine having a hull which is normally atleast partly submerged in sea water comprising an insulated housingattached to said hull, said hull and said insulating housing havingsimilar openings formed therein and defining a substantially continuouspassage therethrough, a cable for carrying RF energy sealed into saidhousing, a first conductive sleeve embeddeed in said housing andconnected to said cable for RF energy transfer therebetween, said firstconductive sleeve surrounding said opening in said housing, an antennamast formed of insulating material and mounted for recipro cal axialmovement in said passage, an antenna element and a second conductivesleeve embedded in the insulating material of said antenna mast, saidantenna element and said second conductive slceve being elcctricailyconnected together, said first and second conductive sleeves beingclosely spaced but insulated from one another whereby RF energy may becoupled capacitively therebetween.

References Cited in the file of this patent UNITED STATES PATENTS1,715,952 Rostron June 4, 1929 2,300,847 Russel Nov. 3, 1942 2,668,187Von Wald Feb. 2, 1954 2,681,4l2 Webster June 15, 1954 FOREIGN PATENTS524,652 Great Britain Aug. 12, 1940

2. AN ANTENNA SYSTEM FOR A SUBMARINE HAVING A HULL WHICH IS NORMALLY ATLEAST PARTLY SUBMERGED IN SEA WATER COMPRISING AN INSULATED HOUSINGATTACHED TO SAID HULL, SAID HULL AND SAID INSULATING HOUSING HAVINGSIMILAR OPENINGS FORMED THEREIN AND DEFINING A SUBSTANTIALLY CONTINUOUSPASSAGE THERETHROUGH, A CABLE FOR CARRYING RF ENERGY SEALED INTO SAIDHOUSING, A FIRST CONDUCTIVE SLEEVE EMBEDDED IN SAID HOUSING ANDCONNECTED TO SAID CABLE FOR RF ENERGY TRANSFER THEREBETWEEN, SAID FIRSTCONDUCTIVE SLEEVE SURROUNDING SAID OPENING IN SAID HOUSING, AN ANTENNAMAST FORMED OF INSULATING MATERIAL AND MOUNTED FOR RECIPROCAL AXIALMOVEMENT IN SAID PASSAGE, AN ANTENNA ELEMENT AND A SECOND CONDUCTIVESLEEVE EMBEDDED IN THE INSULATING MATERIAL OF SAID ANTENNA MAST, SAIDANTENNA ELEMENT AND SAID SECOND CONDUCTIVE SLEEVE BEING ELECTRICALLYCONNECTED TOGETHER, SAID FIRST AND SECOND CONDUCTIVE SLEEVES BEINGCLOSELY SPACED BUT INSULATED FROM ONE ANOTHER WHEREBY RF ENERGY MAY BECOUPLED CAPACITIVELY THEREBETWEEN.